The break between the scientific comprehension of time as well as our general knowledge of time has bothered thinkers all through history. It has deepened since physicists have slowly stripped time of most of the characteristics we usually ascribe to it. Now the rift between the time of physics and the time of experience is approaching its logical conclusion, for many people in theoretical physics have come to believe time essentially does not even exist!
The concept of a timeless reality is at first so staggering that it is difficult to see just how it may be consistent. Every thing we do, we do in time. The world is a line of events strung with each other by time. Anybody can observe that objects move. We notice change, and change is the variation of attributes related to time. Without time, the world is actually completely still. A timeless theory confronts the dilemma of explaining why we see change if the world is not really changing.
Latest research tries to perform only this feat. While time might not exist at a primary level, it may appear at higher levels—just as a desk can feel solid despite the fact that it really is a swarm of particles made of mainly empty space. Solidity is a collective, or emergent, asset of the particles. Time, as well, could be an emergent asset of no matter what the key components of the world are.
This idea of emergent time is possibly as revolutionary as the development of the theories of relativity and of quantum mechanics a century ago.
Our rich commonsensical notions of time have suffered a withering number of demotions all through the centuries. Time has loads of tasks to perform in physics, but since physics has evolved, these tasks have been outsourced one after the other.
Isaac Newton’s laws
It might initially not be noticeable, but Isaac Newton’s laws of motion need time to have many particular capabilities. All observers in principle agree on the series wherein events occur. No matter when or where an event happens, traditional physics assumes that you could objectively say whether it happens before, after or at the same time with any other event in the universe. Time consequently offers an entire ordering of all the events in the world.
Simultaneity is absolute—an observer-independent fact. Moreover, time has to be continuous to ensure that we can determine speed and acceleration. Classical time must also have a notion of duration—what physicists call a metric— so that we can tell how far apart in time events are from one another.
Newton’s time may look like old hat to us now, but a moment’s contemplation shows just how amazing it is. Its many features—order, continuity, duration, simultaneity, flow and the arrow—are logically detachable, yet they all stick together in the master clock that Newton named “time.” This set up of features succeeded so well that it lasted untouched for almost two centuries.
Then came the assaults of the late 19th and early 20th centuries. The very first was the work of Austrian physicist Ludwig Boltzmann, who reasoned that, mainly because Newton’s laws work equally well going forward or backward in time, time does not have any built-in arrow. Instead he suggested that the difference between past and future is not intrinsic to time but derives from asymmetries in how the matter in the universe is organized. Although physicists still debate the details of this proposal, Boltzmann convincingly plucked away one feature of Newtonian time.
According to the special theory of relativity, what events are happening at the same time depends on how fast you are going. The true arena of events is not time or space, but their union: space time. Two observers moving at different velocities disagree on when and where an event occurs, but they agree on its space time location.
Gravity distorts time
Things just get worse in 1915 with Einstein’s general theory of relativity, which stretches special relativity to situations where the force of gravity operates. Gravity distorts time, so that a second’s passage here might not imply the same thing as a second’s passage there. Only in exceptional conditions is it possible to synchronize clocks and have them stay synchronized, even in principle. You cannot routinely consider the world as unfolding, tick by tick, based on a single time parameter. In extreme circumstances, the world might not be carvable into instants of time at all. It then becomes impossible to claim an event occurred before or after another.
General relativity consists of many functions with the English word “time” attached to them: coordinate time, proper time, global time. Together they carry out many of the tasks Newton’s single time did, but individually none of them seems worthy of the label.
Either the physics does not listen to these clocks, or, if it does, those clocks apply only to small patches of the universe or to particular observers. Although physicists today fret that a unified theory will have to eliminate time, a good argument can be made that time was already lost by 1915 and that we just have not fully come to grips with it yet.
Even if the world is fundamentally timeless, still it seems as though it does have time in it. An urgent question for anyone espousing timeless quantum gravity is explaining why the world seems temporal.
Time may exist only by breaking the world into subsystems and looking at what ties them together. In this picture, physical time emerges by virtue of our thinking ourselves as separate from everything else.